Ball bearings are used to support the wheels of vehicles. The ball bearings have an inner race, an outer race and a plurality of balls housed in a separator or cage between the races. Ball race surfaces are machined in the inner and outer races. These surfaces are ground to provide close tolerances of size, surface finish and roundness. This will produce a smooth rolling surface for the balls. The grinding process can produce evenly spaced lobes, on either the inner or outer race, of very small amplitude and continue to be acceptable within the roundness tolerances. This lobing effect induces an impulse each time a ball passes over one of the lobes. This impulse can be significant when a number of lobes are simultaneously aligned with respective ones of the balls. Since the balls are evenly spaced in a separator, the impulse created thereby will be very significant if the number of lobes is a whole number multiple of the number of balls in the bearing.
The frequency of the impulses varies with the rotary speed of the wheel being supported. If the frequency of the impulses approaches the resonant frequency of the suspension system supporting the vehicle on the wheel, the induced vibration will become very noticeable in the form of noise and vibration. With the current technology in suspension design, the elements of the suspension tend to be lighter and stiffer.
One solution that has been proposed and is in use is the imposition of tighter tolerance limits on the roundness specification of the races. This tolerance tightening results in the need for one-hundred percent (100%) inspection on a tracing apparatus. This is an expensive procedure and is not practical in a high volume manufacturing environment. In lieu of this procedure, periodic inspections are performed to insure the process is under control. However, this can miss some bearing races with excess lobing.